Characterization of an aflatoxin biosynthetic gene and resistance in maize seeds to Aspergillus flavus

Abstract

Crop contamination with aflatoxins produced Aspergillus flavus and Aspergillus parasiticus is a persistent problem. A review of the literature on compounds that inhibit aflatoxin biosynthesis showed that many inhibitors are plant-derived and some may be amenable to pathway engineering for defense against aflatoxin contamination. Other compounds showed promise as storage protectants. Inhibitors with different modes of action could be used in transcriptional and metabolomic profiling experiments to identify regulatory networks controlling aflatoxin biosynthesis. Liquid chromatography was used to characterize a protein fraction from kernels of the resistant maize line Tex6 that inhibits growth and aflatoxin production by A. flavus in vitro. Two proteins were associated with the inhibitory activity. Peptide sequencing identified them as chitinase A (ChitA) and zeamatin, members of the glycoside hydrolase 19 (GH19) and thaumatin-like protein (TLP) families, respectively. Removal of chitin-binding proteins from the fraction dramatically reduced its inhibitory effect. Adding the chitin-binding fraction back to the zeamatin-enriched fraction restored activity. We used bioinformatic, phylogenetic and gene expression analyses to investigate the GH19 and TLP gene families in maize. Phylogenetic analyses placed the maize GH19 genes into four major phylogenetic groups. The TLP gene family was larger and was similar to the rice TLP family. Transcripts of members of each gene family were induced during A. flavus infection of kernels.